Blow By Question

[Mr. BILL]

Today I saw an ad for a '81 300SD.It is supposed to have a good body and interior, new brakes and tires. the ad also said the engine was rebuilt 150K ago and is experiencing blow by.

My question is, how significant is this ailment? I'm considering this as a car for my son to drive to school ect. Will it get worse and require bottom end work? What are the consequences of driving it? What am I looking at to correct?

I can pick this car up for about $1000.00

Excessive blow by typically means complete engine overhaul time. To have one overhauled would be at least $4,000 at an independent shop.

Good luck,

[Mr. BILL]

Larry,

Thanks for your reply. Is this something that can be driven with a sacrifice of power, or will it cause the engine to crap out?

As I said, I'm looking for a driver for my son to go to school. At some point I may consider a junk yard motor oruse this one as a parts car. The body and interior are good.

I'm only interested because it's cheap.

Blowby alone could work as a driver, the only problem is when the compression gets too low for the engine to start. Compression is what you're looking for.

The good news with a diesel engine is that as long as you have enough compression for the engine to start and can carry enough oil to get where you're going, you can continue to drive the car. A gas engine burns valves, fouls spark plugs and other ills. The bad news is that if it does get to the point of needing a rebuild, it is typically much more expensive to drive a diesel.

I would suggest that you do a compression check on this engine. If the compression is 300PSI or better on all cylinders, the blow by itself will not pose a problem that will prevent the car from being drivable. Typically excessive blowby will go along with low compression. But it could be that excessive oil consumption will not prevent the car from starting and running.

You should do two things, see that the compression is up and that the car starts when cold. I have heard of people using the block heater to start the car so they can sell it to an unsuspecting buyer. Don't get caught by that one. Before you start the cold engine, feel of the engine to ensure that it is indeed cold.

If it starts easily when dead cold, and I mean overnight cold, and it has good compression, you MIGHT get by with this for your purpose as long as your son understands the necessity to constantly check the oil and keep it full.

If you do buy a serious oil burner, don't believe the old wives tale that the oil changes itself. Contaminants are worse in an oil burning engine, and need oil changes maybe even more frequently than a healthy engine.

All that said, I really don't recommend that you go down this road. You may very likely spend more on this car in the long run than if you had spent more money up front for a solid car.

Best of luck and Merry Christmas,

I would never believe what anyone said was wrong with a car until I myself had it looked at. How does the seller know it has blow-by? If it is worth it to you, have it looked at by a mechanic. You may find it is leaking oil, or has a leaky turbo, or some other problem instead.
I once bought a Jeep for pennies that the owner claimed needed a new engine. A local mechanic told him this. I looked at the Jeep, the engine, the fluids. I was told it didn't start, just turned over endlessly. I towed it home, proceeded to do a tune up and by the time I got to the spark plugs, I realized that the wires were not in the proper order on the distributor cap. I switched them around, gave the key a turn, and it started right up, purred like a kitten, and had great compression. I took a chance, and it turned out okay. If it isn't proven it has blow-by, it may be worth a shot.

patsy is absolutely right, but unless you can determine ahead of time the actual condition, you need to proceed carefully.

Now for one of my infamous long winded stories that patsy's post reminded me of;

In the mid seventies I built a new house and needed a pickup to haul sod, building material, etc. I found an old '65 Ford six cylinder, the guy was asking $400( you can tell this was a long time ago). It would stumble on acceleration and wouldn't run right at all. It didn't seem to have anything seriously wrong with it in any other way. I waited the guy out. Noone wanted to buy it because it wouldn't run right.

I finally got it for $100 and drove it slowly home. I checked the timing and vacuum advance, then I started doing exploratory surgery on the carburetor. I took the air horn off the carburetor and it was very obvious what was wrong. The gasket was backwards which interfered with the accelerator pump. I turned over the gasket and the thing ran great. I repainted the truck in the driveway, and it turned out to be a really nice truck. I did nothing to it but oil changes and tune ups and sold it a few years later for $1,000.

This can happen, check the car out and proceed with caution. Even though this kind of thing can happen. You can't plan on a miracle every time. If you were to check compression and find it up to snuff, the problem could easily be elsewhere.

If something like this were to work out for you, make sure you thank patsy.

Good luck,